If you have registered a Protocol that will provide a lot of the initial information you need for the final paper.
The paper should be written following the instructions set out in the PRISMA Statement 2020, particularly:
The flow diagram is an important part of the paper. If you have used Covidence systematic review software you can take advantage of their flow chart, but keep in mind that it does not include everything and needs to be edited - see https://library.svhm.org.au/systematic-reviews/covidenceflowchart