I understand that you need to offload SSL somewhere.
The first option is to do SSL offload with the sidecar.
https://learn.microsoft.com/ja-jp/azure/container-instances/container-instances-container-group-ssl
You need a deployment that includes a sidecar container to ACI.
If this is difficult, look for other ways to offload SSL.
It may be possible using Azure managed services.
The Azure Front Door / Azure Application Gateway L7 load balancer provides SSL termination.
I think that the traffic received by HTTPS with these services can be forwarded to ACI by HTTP.
However, when using this, you need to think about how to control direct access over HTTP.