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do u know what should we do if some one lost his rc abroad so he needs to apply for single entry visa uk or eea family permit they r unmarried partners as well so what he needs to do they contact to british high comission but they did nt give any reasonable answer

I'm not sure about unmarried partners, but I know one real example of married couple.
She lost her RC while visiting her parents with her husband in country outside EU.
So they had to apply for Family Permit, and after coming to the UK new EEA2 application was submitted.

British High Commissioner will all due respect has got nothing to do with that, I believe. As unmarried partner is most probably not UK citizen, so the question should be directed to Visa Section of the embassy.

No point in making enquiries.

An EEA family permit application is what that is needed.

An EEA family permit can only be issued to An extended family member if in all the Circumstances it is appropriate for the ECO to do so.

You will need to argue that the person is a family member within the meaning of regulation 7 (3).

I am a 5 years Residence Card holder as married to an EEA citizen residing in the UK.

I lost my RC while traveling abroad last February.
I explained to a boarder officer in the UK that I had lost my RC while traveling, but I was allowed to pass the boarder quite easily, probably because I was with my EEA husband.
The officer advised me to apply for the Resident Card again, but I was not willing to do it, since I would be eligible to apply for the PR last December.

Since I lost my original RC last February, I traveled abroad 3times carrying a copy of the RC, marriage certificate and proof of dwelling with my EEA husband, and a printed out webpage from UKVI website describing as "You don’t need a residence card to live in the UK, but it can....".
After all, no officer has asked me to show those extra documents.

I applied for the PR a couple of weeks ago,and have been waiting for it.

The OP case is different as he is unmarried partner so can make it more complex to him at the border.

A lost residence does not necessarily equate to an expired residence.
There may be an argument that Regulation 7 (3) continues to apply.