I think there is not an option in writer to set separator symbol in tools>outline numbering, si i explain my request (that i think it is request of many libre writer users)
in sub level outline we need to use different symbol instead of dot symbol, like this:
1.
1-1.
1-1-1.
1-1-2.
1-1-2-1.
…
there must be a field to set tis symbol.
thanks
NO, it is not possible to do what you said, in fact after and before fields effect on all outline , if you test yourself will see how it works 
(so so sadly)
@NasserMansouri, you did not read my answer correctly. I said it “cannot” be done. I then provided a reason as to why it cannot be done.
Bug 70006 - FORMATTING: define separator in tools>outline numbering
Probably a duplicate of
Bug 67986 - EDITING: FORMATTING: ENHANCEMENT: Choose characters of each SEPARATOR between numbers in Outline Numbering.
See also:
Bug 21387 - Specify separator characters BETWEEN numbers in outline numbering –
OOo 1.1 RC5 · 2003-10-18
fdo#70006 has been marked as a duplicate of fdo#67986 · Status: NEW
You are correct in that you cannot set the outline numbering of heading levels in the manner you desire. The reason is because in your example “1.” is equivalent to the “1-” part of the “1-1.” leading identifier i.e., the character that comes after the identifier of the level 1 heading would need to change from a “.” to a “-” depending on the level of the heading in which it is being used.
If you desire this form of leading identifier arrangement all I can suggest is you raise a bug and include as much detail as possible in your description. Please post a link back here to any bug raised using the form “fdo#123456”. Thanks.