To remove you as a dependent he will have to file a 2019 federal amended tax return, Form 1040X. He would have to pay back the $500 Other Dependent credit he received on the federal tax return for claiming you as a dependent.
If he amends his tax return, you will not be able to apply for the stimulus payment until after his 2019 amended return has been processed by the IRS. In a normal year the IRS takes about 4 months to process an amended return. Due to the pandemic and limited staffing the IRS is taking much, much longer to process paper tax returns.
