Oracle 18c

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create table temp
(
indicator nvarchar2(80)
)
INSERT INTO temp
SELECT 
'GB-JP--123456vvvv' from dual
UNION ALL
SELECT '401015 - GB-NA' from dual
UNION ALL
SELECT '1' from dual
UNION ALL
SELECT '999999 - LX - UK' from dual

4 rows affected

select regexp_replace(indicator, '[^0-9]', '') from temp


REGEXP_REPLACE(INDICATOR,'[^0-9]','')


123456

401015

1

999999