how to disable bitlocker with key but no admin access?

[plucky wing]

you don't. however, you can unlock the encrypted the drive.

[twilit dew]

how can I do that?

[plucky wing]

When you're prompted to do so? I have a gut feeling you're dealing with something that doesn't belong to you.

[native kiln]

Have you considered talking to your Admin about this?

They can disable it for you

[twilit dew]

it isn’t

Strict parents

Im not stealing anything im doing this to dual boot windows

That’s why so if i get caught I can switch back

Nothing bad im just a geeky kid

[native kiln]

You can do this without disabling bitlocker. Shrink the partition and then create a new partition

[plucky wing]

A Bitlocker encrypted volume needed to be decrypted in order to be resized (in Disk Management/diskpart). I think OP already realized that fact. Hence, the question asked.
Extending without decrypting may lead to corrupt partition/performance issues.

[twilit dew]

better than a fucking crime

[twilit dew]

in the windows install process if you wanna install anything you gotta unlock your drive

[native kiln]

that is not true, you can do this without disabling bitlocker.