The phrase "attach his" is correct and usable in written English.
It can be used when referring to the action of connecting or affixing something belonging to a male individual.
Example: "Please attach his signature to the document before submitting it."
Alternatives: "affix his" or "join his".
He declined to attach his name to the paper.
Then he got out and leaned against the trunk to attach his stilts.
Finally, Iversen recognized the precise place where he could attach his compound.
It turned out that the man had failed to properly attach his safety harness.
What prompted him to attach his persona to this abysmal piece of stale cheese?
And you'll know why Nathan Lane was glad to attach his name to this delightful show as producer and presenter.
He has undergone a seven-hour operation to re-attach his partially severed hand and was kept in an induced coma following the procedure.
The shock news that Ryan Giggs was to be cloned was announced by Sir Alex Ferguson in 2014, encouraged by stem-cell research that helped to reshape his nose and re-attach his chin.
Rather he attached his seal to it.
Did Thunder sit still while a volunteer attached his leash?
Before the final race, Mattress jumped into his car, attached his harness and lighted a cigar.
