Passport for child born abroad

[RUSOH]

Hi There
Need some suggestions

My child was born abroad and gilded Indian Passport
His last and forename was in the last name column with empty forename .

He got British passport with same pattern of name 1 month Back.

Got a deed pole done , with supporting letters from school And GP surgery regarding splitting of his name .

Now when I applied to split his On British passport separately , they say it’s not possible as he needs to get it changed in Indian passport first.

He is 12 and he has already received his British passport how can Indian embasey change his name .
Of course I will surrender his name .

What to do , please advise

Thanks