IRS publishes the formula for how to calculate the gain or loss.
It can be a messy calculation so that is why the custodian is expected to do it.
You can look up the formula, do the arithmetic and then take out the calculated amount as a withdrawal.
You'll have to explain what you did on your 1040-X.
You are undoing $7,000 dollar not-deductible contribution, so that is the amount you must enter to unwind it
@shr22
