Either
=TEXT(LEFT(A1,5),"0000000")&"-"&TEXT(RIGHT(A1),"000")
to have the values as text.
Or, pre format the cells in the column that is to take the new values with
Format>Cells>Number>Custom> 0000000-000
then
=--LEFT(A1,5)*1000+--RIGHT(A1)
to keep it as a number
If your existing values are not in column A, change as appropriate.
Drag the formula down the receiving column as far as required.