If he filed his return and you are shown on his tax return form 1040 as a dependent, then he in fact claimed you. If his return was accepted, he will have to prepare, print and mail an amended return form 1040X to delete you from his return. He should not delete you before he starts the amended return. Here is a link to help with amending: https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
Amended returns must be printed and mailed. They can't be efiled. He must print, sign and mail it himself. In normal times it takes the IRS about 16 weeks to process an amended return.
He should never have been able to claim you if you had more than $4200 of income. Have you filed your own return and did you check the box that you could be claimed as a dependent by someone else? If you did, you will not be eligible for the stimulus payment unless you also file an amended return to uncheck the box.
