You can never rollover an RMD into another IRA, unless the prior owner was your spouse.
If the prior owner was your spouse, the rollover should not be taxable. What code is in box 7 of the 1099-R? When you enter the 1099-R, don't skip to something else, keep going in the interview and you will eventually be asked if you inherited this IRA, and what you did with the money, rollover should be one of the choices.
If the prior owner was not your spouse, you can never do a rollover into your own IRA. You must take a withdrawal and pay the taxes. Then, you could contribute some money to your own IRA and take a tax deduction, if you meet the normal eligibility rules. But the withdrawal and the contribution are two separate transactions that must each follow their own rules.
A rollover from an inherited IRA into your own IRA is an illegal transaction, and I'm not sure what the
consequences are, @dmertz ??
