Please Help with add new formВ from lookup field in formA

Please Help with add new formВ from lookup field in formA

I have bideraction lookup with FormA and FormB. And want to add new FormB from lookup field in formA.

After saving (or when i creating it), i want to fill some field.
I use script (in formB) on Add --> on Success:

"docs = FormA [ FormB == input.ID ];
for each rec in docs
{
insert into addSprava
[
promizhnuyRezult = rec.sender_field
]
}"
But it doesn't work.
 Please help me with this issue.