Who volunteers to make sure Caesar goes out to the Capitol the next day?

In Act II, Scene 1 the conspirators are firming up their plans to assassinate Julius Caesar the next morning when he is supposed to go to the Senate House at the Capitol expecting to be crowned king. Cassius expresses some apprehension. He suggests that Caesar may decide not to come because of:

...these apparent prodigies,
The unaccustomed terror of this night,
And the persuasion of his augurers...

At this point the conspirators do not even know about Calpurnia's bad dream which will cause her to plead with her husband not to leave the house.

It is Decius who volunteers that Caesar will go to the Capitol the next day. He tells the others:

Never fear that. If he be so resolved
I can o'ersway him....
Let me work,
For I can give his humor the true bent,
And I will bring him to the Capitol.

In Act II, Scene 2, Cassius' foresight proves, as usual, correct. A servant tells Caesar that the augurers have found bad omens.

They would not have you stir forth today.
Plucking the entrails of an offering forth,
They could not find a heart within the beast. 

But it is Calpurnia's dream and her begging him to stay at home that make the strongest impression on Caesar. He tells Decius:

Calpurnia here, my wife, stays me at home;
She dreamt tonight she saw my statue,
Which like a fountain with an hundred spouts,
Did run pure blood, and many lusty Romans
Came smiling and did bathe their hands in it.
And these does she apply for warnings and portents
And evils imminent, and on her knee
Hath begg'd that I will stay at home today.

This was unexpected because Calpurnia had only had that dream a few hours earlier. But Decius shows himself shrewd and adaptable. He tells Caesar:

This dream is all amiss interpreted;
It was a vision fair and fortunate.
Your statue spouting blood in many pipes,
In which so many smiling Romans bathed,
Signifies that from you great Rome shall suck
Reviving blood, and that great men shall press
For tinctures, stains, relics, and cognizance.
This by Calpurnia's dream is signified.

Any dream can be interpreted in different ways. Caesar likes Decius' interpretation. He would like anything that would encourage him to go to the Capitol because he wants to be crowned king. He would tend to discount any omen that would warn him not to go to the Capitol. Decius knows this. He plays on Caesar's ambition by following up on his interpretation of Calpurnia's dream with a carrot and a stick, so to speak. He tells Caesar the crown is waiting for him but that the senators could change their minds if he failed to show up that morning. They might believe that he doesn't really want the crown, or they might feel insulted because they were all waiting for him and he disdained to appear. As Decius puts it:

If you shall send them word you will not come,
Their minds may change. Besides, it were a mock
Apt to be render'd, for some one to say
“Break up the Senate till another time,
When Caesar's wife shall meet with better dreams.”
If Caesar hide himself, shall they not whisper
“Lo, Caesar is afraid”?

Caesar is convinced. He tells his wife:

How foolish do your fears seem now, Calpurnia!
I am ashamed I did yield to them.
Give me my robe, for I will go.

The scene might be expected to end here, but there is some incidental dialogue before it finally does. During this time one of the servants will go offstage to get Caesar's robe, return with it, and help him put it on. The robe will be very important. It may be of a distinctive color which makes it stand out among all the other men's robes at the Capitol. When Antony shows a robe to the mob during his funeral oration, it will be a duplicate. It will appear to be the same robe Caesar put on in Act II, Scene 2, but this duplicate robe will be totally ruined with dirt, shreds and bloodstains. Caesar's body will not be seen by the audience but only his robe, which will represent his hacked and bloody body. The plebeians who look down into the coffin will supposedly be seeing Caesar's body and reacting to the pitiful sight, but the theater audience will only be seeing the duplicate robe, which Mark Antony will be holding up in full view. Among other things, the duplicate robe will remind the theater audience that Calpurnia was right in trying to keep her husband at home and Caesar wrong to listen to Decius.