The stop leak is a re-charge...sorta. You probably need the recharge kit with the charging hose:
https://www.canadiantire.ca/en/pdp/red-tek-a-c-refrigerant-recharge-kit-0146129p.html#srpWhat I do is connect the hose and see where the pressure is at, if there's nothing, and the compressor isn't coming on, then put one can of the refrigerant in. IF the compressor starts to cycle, then you're in business, if not, then you've got a problem somewhere else...
Once you've got the compressor cycling, then install the stop leak...there are two versions, I can't remember which I used, I'd probably spend the few $ and get the pro-seal though:
https://www.canadiantire.ca/en/pdp/red-tek-aerosol-leak-stop-can-4-z-0146121p.html#srpOnce that's in, if the pressure is still on the low side, then add the second can of refrigerant...or part of it until you're getting stable pressures in the 'green' area on the gauge.
^That's a pretty half assed instruction, but there are a ton of videos and stuff out there on this. It's not hard, I've done it dozens of times (usually for co-workers and stuff) so if you need help PM me.