Replace character using regexp_replace after and before character

Consider:

regexp_replace(mycol,'0+','-', 1, 1)

Rationale: the fifth parameter, when greater than 0, specifies wich occurence should be replaced; when it is set to 0, all occurences are replaced.

Other notable changes to your original regex:

• parentheses define capturing group; since you don't need to capture, there are superfluous
• brackets define a character class; not needed since you are matching on a single character

Demo on DB Fiddle:

with a as (
    select '30000001174934177910' mycol from dual
    union all select '30000000174934177910' from dual
    union all select '301873130520' from dual
    union all select '300173130520' from dual
)
select mycol input, regexp_replace(mycol,'0+','-', 1, 1) output from a

INPUT                | OUTPUT         
:------------------- | :--------------
30000001174934177910 | 3-1174934177910
30000000174934177910 | 3-174934177910 
301873130520         | 3-1873130520   
300173130520         | 3-173130520