I just want to use the relative URI in the ICAP profile

Hi Wasfi_Bounni , 
Well , you can use this macro at URI field in ICAP profile configuration: 

 icap://${SERVER_IP}:${SERVER_PORT}/path

Using this Macro will replace ( ${SERVER_IP} by Selected Icap member ip from ICAP pool which you assigned to internal virtual server , and ${SERVER_PORT} Will follow the same mechnism. 

Please Follow this Offical Article step by step in your implementation : 

https://techdocs.f5.com/en-us/bigip-14-0-0/big-ip-local-traffic-manager-implementations-14-0-0/configuring-content-adaptation-for-http-requests-and-responses.html

you will find all steps on details on it , or you can use it as a reference to review your configs. 

Goodluck 🙂