As per your example:

In Find type: ([0-9]@)(h)
in Replace type: \1 \2
Note that there is a single space just after the 1.
Click More>> and check Use wildcards
Click Replace All
It means:
Find one or more number ([0-9]@) followed by a lowercase h (h)
Replace with: same first element found (the numbers) \1 add a space " " then same second element found (the h) \2

***Never do testing on original files*** unless you can do an Undo .