You enter the 1099-R:

https://accountants.intuit.com/support/en-us/help-article/retirement-tax-credits-deductions/report-c...

The "backdoor" refers to the initial Trad IRA contribution being nondeductible. That way, the conversion to Roth is all basis; and, it is done nearly immediately, so that there were no earnings on the Trad IRA in between the contribution and the conversion.

If they have any other funds in Trad IRA, SEP IRA, or SIMPLE IRA with other than Basis, now you don't have Backdoor. You have a pro rated taxable conversion.