Unlocking a normal smartwatch is not a big problem but the problem is what exactly do you mean by unlocking. If you are talking about just unlocking, then just press the unlock button which is set for this particular task.
In your smartwatch manual, you will see that there is a particular button that unlocks the smartwatch. But if your smartwatch is so smart that you actually put a password and then forgot what you have put as a password then that is the problem you need to find a solution for.
You need to find your instruction manual. It is very important. There will definitely be instructions about hard-resetting your smartwatch.
Now, if you have bought or got the smartwatch from someone and there is no instruction manual, then you have to find the make and model of your smartwatch and then do a bit of research online to find out how to factory reset or hard-reset your smartwatch. This is the answer to your questions. We hope this helps.