Like others have said you will need a chain tool. If you have the original chain count the links. The length depends on the length of the chain stays, cassette cog range, chain rings and derailleur. If the have not changed why reinvented length. Knowing the number of links will ensure you buy enough chain. Realistically any off the shelf 7 to 8 speed chain will work. A quick link should come with the chain to join the ends on the bike.

KMC makes good chains and come with a quick link. Here is one on Amazon.

https://a.co/d/3bNdGQr