If you filed using TurboTax, TurboTax would have limited your self-employed retirement deduction to only that which was allowed, so there is nothing to change on you 2018 individual tax return.
Yes, the excess can be applied as part of your 2019 SEP contribution and you can deduct it on your 2019 tax return. See IRS Pub 560 page 7:
https://www.irs.gov/publications/p560#en_US_2019_publink10008842
Nothing else is required. with regard to the IRS (except, perhaps, to provide explanation if the IRS questions the amount reported as your self-employed retirement deduction for 2019). To get TurboTax to include the carryover as part of your self-employed retirement contribution on line 15 of your 2019 Schedule 1, when entering the amount of your SEP contribution for 2019 include the amount of the carryover.
