I use wordpress multisite and domain mapping. My

Hello, I use wordpress multisite and domain mapping.
My sub-domain( 1.example.com )mapped to this ( mydomain.com )domain name.
My question is,
mydomain.com/contact this page only i want redirect to 1.examble.com/contact ( original sub domain )
How this can be done?
i already asked this question multisite category. But i still not get any useful answers.
Anyone please help.
https://premium.wpmudev.org/forums/topic/i-use-wordpress-multisite-and-domain-mapping-my