5 Pack Bathtub Jet Covers 22mm 7/8 inch Jetted Tub Jet Port Plugs Silicone Stopper Caps Seals Soaking Hot Tub Adapter for Spa Hot Tub Storm Jets Diffuser Bath Jets Air Bubble Outlet Hole

https://www.amazon.com/UtySty-Silicone-Bathtub-Furniture-Waterproof/dp/B0BWTB1DXM?th=1 measure the jets, and see if something like this is available in the appropriate size? I doubt its totally watertight though. You could put them in with marine sealant? edit:Here's someone that did a custom thing with doorknob covers and marine sealant? https://thecozyloft.wordpress.com/2017/01/24/jetted-to-soaker-tub-conversion/