IRS released the below Frequently Asked Questions (FAQs), and provided a new Form 7200 for employers to apply for a refund of their credits in excess of their payroll tax deposits.

FAQ sick leave credits
FAQ retention credits
Form 7200
 
Employers should first reduce employment tax deposits to account for the credits, and may receive any additional refund when filing their quarterly employment tax returns. Filing Form 7200 will cause employers to reconcile advance credit payments and reduced deposits on their employment tax returns. Form 7200 is not a required filing and should only be used to obtain an advance payment for credits.
 
Per the instructions to Form 7200, the form is filed by faxing it to the IRS.