Sharepoint workflow for approval

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New to sharepoint

I have small process

User manager1 manager2 director

step 1 User submit form
If field set to new,go to director-->> approval task
else
step 2 if field set to Old
goto manager1, manager will update form THEN -->> go to manager2, manager2 will update form THEN goto director for Approval

in form manager1 update field should be enable only to manager1
and manager2 field should be enable to manager2 only

please help.

What I have tried:

New to sharepoint
i cannot enable manager1 fields for manager1, and same for manager2