You can book it through Thrillophillia. They have complete package of water sports and dry activities. Also you can ask for discounts if in a large group.
here is a video for your reference. https://youtu.be/7-R8y5LzjwI
No need for covid certificate to visit goa or anywhere until unless u get through mumbai route and vividh test is necessary only if u get out of mumbai airport.
Best Wishes