Hold custom screen data till save on MB1B

I have created a custom screen between two standard screen of MB1B.

I want to keep the data entered by user on the screen till user is in MB1B transaction.

i.e

On MB1B,

first screen : User will enter data and next

Custom screen : User will enter data and next

Second screen : user will enter data and save or Back.

Afterr go back from second screen my custom screen will appear, But currently I am unable to hold the entered data on custom screen.

What I have to do?

Please suggest.

Thanks,

Monika