Below worked for me with Helm-3:
Step-1 : helm search repo mongo -l
( Assuming you have already done helm repo add bitnami https://charts.bitnami.com/bitnami)
Step-2 : Check the mongo version you want to install and note the corresponding latest chart version
Step-3 : Use the chart version from above to install the specific version of mongoDB using –version.
helm install my-mongodb bitnami/mongodb --version 8.3.1
Note : 8.3.1 is the chart version not mongoDB version