If you have written down the 15 word Seed Phrase or Back up Phrase, for your Waves wallet, you can always access it by importing the phrase.
If you have made a new account, log into that account then at the top right click on your avatar and choose “Switch Account”
Then click on Add Account.
In the middle of the screen click on "Import Accounts".
On the next page click on "Seed or Key".
Enter your 15 word "Seed Phrase" into the space as indicated by the arrow, be sure you spell each correctly leave one space between.
The words must be in the same order as given when you wrote them down from your wallet.
If you have entered all 15 words correctly and in order your wallet address will appear.
Click on "Continue".
Now give the account a name and click on "Continue"
You will then be in your account and can see all wallets and balances.
You can also see these instructions for both mobile and computer by watching this video.