OK. Makes life easier. In Control Panel, up in the right corner it says View by: The default is Category which is useless. Change it to Large Icons. Now scroll down to System and click on it. In the left pane you will find:
Advanced System Settings. Click on it. At the bottom of the new window will be Environmental Variables. Click on that. In the bottom half of the next window you will see System Variables. Use the scroll bar to slide down to where it says Path. Click on it then hit Edit. Another window will open. It will say:
Variable name: Path
Variable value: This will be blue. Hit the right arrow key on your keyboard. That should put the cursor at the end of the line. Type:
;C:\Program Files\Firebird\Firebird_3_0
(Note the semi-colon at the beginning. Only SPACE is between Program and Files)
Then hit OK, OK, OK and close the System window. See if you still get the same error.