You could use either regular expressions or substr/instr:

with rws as (
  select 'I01 I0102 TID6977105' str from dual
)
  select substr ( 
           regexp_substr ( str, 'TID([0-9]){7}' ), 4 
         ) regex,
         substr ( 
           str, instr ( str, 'TID' ) + 3, 7
         ) sub
  from   rws;

REGEX     SUB       
6977105   6977105  

The regex will only return TID followed by seven digits. Whereas substr/instr will return TID followed by any seven characters. So if you want to ensure you only return TID with exactly seven digits after, the regex is safer here.