Mcnett Aquasure or Aquaseal UB will do a decent job but will remove any breathable properties where it is applied so be precise if it's goretex or equivalent, spread it very thinly or it will noticably stiffen the seam.
Seamgrip is an alternative if you'd prioritise flexibility over durability.
If it's goretex or the like Shelby.fi will mail order you heat-seal breathable tape to apply with an iron (there's a lot more to it, so do some reading if you go that route)
In the unlikely event it's an ultra lightweight silicone coated nylon cagoule you'd need Silnet.