which parts of this will i need to change for my custom fields?

You should share the code you are currently editing.

Thanks

i have, its in the original post.

im using the compute field in the studio.

from datetime import datetime, timedelta

from odoo.tools.misc import DEFAULT_SERVER_DATETIME_FORMAT

for record in self:

record[("x_studio_field_CgBpj")] = datetime.strptime(record.x_studio_field_47ZJc, DEFAULT_SERVER_DATETIME_FORMAT) - timedelta(weeks=5)

Try it bro, i don't test it

[tab]record[("x_studio_field_CgBpj")] = datetime.strptime(record.x_studio_field_47ZJc, DEFAULT_SERVER_DATETIME_FORMAT) - timedelta(weeks=5)

My code: pastebin.com/yYTL4E5h

getting the error:

File "/odoo/odoo-server/odoo/tools/safe_eval.py", line 189, in assert_valid_codeobj

raise ValueError("forbidden opcode(s) in %r: %s" % (expr, ', '.join(opname[x] for x in codes)))

ValueError: forbidden opcode(s) in 'from datetime import datetime, timedelta\r\nfrom odoo.tools.misc import DEFAULT_SERVER_DATETIME_FORMAT\r\nfor record in self:\r\n record[("x_studio_field_CgBpj")] = datetime.strptime(record.x_studio_field_47ZJc, DEFAULT_SERVER_DATETIME_FORMAT) - timedelta(weeks=5)': IMPORT_NAME, IMPORT_FROM

Are both fields of the same type? (Datetime or Date). If not, you need to convert it. I tried something similar and this was the problem I had.