Hello,
On this computer, it doesn't have an admin at all, or it has an admin, but you don't know the password?
If it doesn't have admin at all, there's a way to recover admin access.
Hold down Shift key while you choose Windows restart, then go to Troubleshoot > Advanced Options > Startup Settings, click on restart, then choose option 4.
When prompted for password, leave it blank and enter.
When you are in safe mode, hold down windows + r keys, type in netplwiz and press enter.
Then double click on your username, go to Group Membership tab, make it admin.
Restart, log back into your user. You should now have admin access.
If Safe Mode also asks for admin credential and will not let you bypass with the blank password, it means the computer does have an admin user and you probably just don't know its credential. In this scenario, there's no other option but to clean install it to start over. Do backup your data though before you do so. Let me know if this is your case and if you need clean install instruction.