If the location of a drawing is changed, the On-Screen TakeOff system will not be able to find it out its own.
If the pop-up with the warning Unable to open drawing. Please select a new location for the file, then you should be able to change the location by clicking on the 3-dots button.
Note: You may not be able to see the existing measures on the drawing anymore. This is because if the system detects that the file may have changed, it will not acknowledge it as being the same file and measures cannot be moved between drawing versions.