If this these are real numbers - you need to do an arithmetic operation on
them-
enter 97800000000 in an empty cell; copy it; select the cells of interest;
use Edit > Paste Special with Add checked; deete the cell with 97800000000
If the 'numbers' are things like account 'numbers': use formula
=TEXT("978","###")&TEXT(A1,"#######"); copy down the column next to the cell
of interest; now use Copy followed by Edit > Paste Special with Values
checked to convert fromulas to values. Now you can delete the original values.
best wsihes