Here is where you find the files. This may be different for you based on entitlement.
Check the pull down at the top right and make sure it says "Enterprise Software"
On the left select "my downloads"
In the search start typing unif
You should then see a page like this once you select Unified Infrastructure management. It will only show what you are entitled to.
Click on 20.4
You can then download based on the OS you need, Linux or Windows.
We then recommend you upgrade right away to CU8.
I can give you the direct download to those.
UIM CU8 download: https://support.broadcom.com/web/ecx/solutiondetails?aparNo=99111797&os=MULTI-PLATFORM
OC CU8 download: https://support.broadcom.com/web/ecx/solutiondetails?aparNo=99111806&os=MULTI-PLATFORM
Here is a good document on upgrading.
DX UIM Upgrade Guide and Pre-Planning Checklist for 20.4 (broadcom.com)
If you are unable to find the Unified Infrastructure Management download link as shown above, it means you no longer have entitlement and need to contact your CSM to get this corrected. Support has no access to correct this.