with a as  (  
select '98  46134679////1' as before from dual  
union all  
select '98/46134679/1' as before from dual  
union all  
select '98 / 46134679 / 1' as before from dual  
union all  
select '98 ////// 46134679  1' as before from dual  
)   
select a.before, regexp_replace(a.before, '^([0-9][0-9])([ /-])+([0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9])([ /-]+)([0-9])$', '\1-\3-\5') as formatted from a