"exporter plugin" and "unreal datasmith" both are not available in marketplace. can anyone help me to install plugin please?

I have a serious issue on both version of ue4 (19,20). I could not find to download the exporter plugin and datasmith plugin to install inside the engine. but i successfully installed the datasmith exporter for 3ds max. but now the problem arises to import inside the engine.

Based on your comment on this other topic - https://answers.unrealengine.com/questions/846189/datasmith-import-icon-missing.html - I believe you have now resolved the issue.