Ukulele fingering for low G

You need to go into staff properties and adjust the range and the string data.

Actually if you use "Ukelele (Low G)" that shouldn't be needed.

You need to choose the correct ukulele from the list when adding the instrument, or edit the staff properties afterwards. If you type the first few letters of "ukulele" into the search box at the bottom of the instrument window, you'll see the "Low G" version there. But not for tablature, apparently. If you use the linked staff feature, then simply changing the standard notation would also fix the linked tab staff, but it looks like youve elected not to use that (or did you not know you can have linked standard & tab staves?)

To fix your score using the linked staff feature, right click the standard staff, Staff Properties, Change Instrument, Ukulele (Low G). Then, Edit / Instruments, select that staff, Add Linked Staff, and change type to whichever tab style you prefer. Then delete the existing (incorrect) tab staff.

Or, to keep the existing non-linked tab staff but fix the tuning, right-click, Staff Properties, Edit String Data, change the tuning of the low string from G4 to G3.