@Amoghavarsh Patil Apology, looks I misunderstood.
As your APIM is under the Internal VNet, so if you want to integrate Azure Front Door directly with APIM, APIM should be deployed in public internet or deployed as external VNet mode. The APIM instance should be accessible from external load balancer.
The same is documented here and this blog.
Set up an Azure Front Door Standard/Premium profile in front of a publicly accessible Azure API Management instance: either non-networked, or injected in a virtual network in external mode.
I do see front door FAQ here as origin must have a public IP or a DNS hostname that can be resolved publicly