You will need a such as Enso or HENkaku. Official stock firmware does not allow direct file injection for PS1 saves (only cloud backup via PS Plus, which doesn’t support custom files).
or an FTP client through VitaShell to move the downloaded save into the appropriate directory on your Vita. Use Save Manager : If you use tekken 3 all characters unlocked save file psv hot
The fastest way to get every fighter is to download a completed save file and import it into your console. For the PS Vita, this process varies depending on whether you are using the official PS Store version or the emulator for homebrew users. You will need a such as Enso or HENkaku
Here is what a gives you immediately: