Builds of php 7 remove support for older MySQL password encryption methods. If you have an older password, you may need to reset the password to work with php 7. You can use the same password. You simply need to reset it so that MySQL re-encrypts it with the new method. To do this, go to the "database" section of your control panel and select "Change database password"
A complication of changing your database password encryption method arises if you are using php 7 along side an older php version on another part of your site. Changing the password may break the older code if the php version employed uses the previous password encryption method. We recommend you check all other sites on your account to ensure they still work with the new password.
If you find problems, the best resolution is to move all code to a newer php version. If this is not possible, you can also open a second account to run the other site. If you have needs for very old legacy php support (php4, etc.) we can configure a custom VPS to meet your legacy php hosting requirments.