The subscription link is one per account and you import it on every device you own: phone, laptop, TV. What limits you is not the number of imports but the subscription's device counter: every device that reaches your link takes a slot and holds it until you unlink the device. Used and free slots are visible in the My devices section.
On a TV the link is awkward to type with a remote. Copy it on a phone or computer, forward it to yourself (a Telegram message works), and in HAPP on the TV add the profile from the clipboard. On Apple TV the clipboard is shared with an iPhone when both are on the same Apple ID.
Devices are detected automatically when they connect; there is nothing to add by hand. The list shows the platform, the app, the date it first appeared and the last activity. Devices that have not been in touch for a long time are marked stale and eventually drop off the list on their own.
Open the My devices section, find the device you do not need and unlink it. The slot frees up right away and that device loses VPN access; it can connect again through the subscription link if you need it to, taking a slot again. The same move covers changing phone or reinstalling the system.
If every slot is taken and there is nothing to unlink, the number of devices is chosen when you subscribe in the payment section.
You can share the subscription with the people close to you in the VPN sharing section. Their access rests on the payer's active subscription: while it is active, everyone connected to it works.
Do not give the subscription link to anyone else. It is personal and it opens your subscription: other people's connections take your slots, and you end up seeing devices you do not recognise in the list. If that happens, unlink them in the My devices section.