This is an error that is complicated to correct, made worse by the amount of time that has elapsed. The IRS provides no specific guidance on correcting this, but it's not something that could have been corrected by simple recharacterization. Because a traditional IRA is not an account that is eligible to receive a rollover from a Roth 401(k), this is technically a failed rollover and a regular, probably excess contribution to the traditional IRA subject to penalty. Seek the help of a tax professional who has experience with this situation, although one might be hard to find. It may be possible to correct this by obtaining a distribution from the traditional IRA of the excess contribution (after the due date of your 2019 tax return) and completing the rollover to a Roth IRA under self-certification under IRS Notice 2016-47 that this would qualify for a waiver of the 60-day rollover deadline, but that wouldn't avoid an excess contribution penalty for 2019 (and for 2020 as will since this will likely not get resolved by December 31, 2020). You'll have to amend your 2019 tax return no matter what you do.
