How to do a cohort analysis using a heatmap

I tried to find a solution online, but I haven't found any answer yet. I am trying to do a cohort/ customer retention analysis. The picture shows my take on this. What I want:
I want to see whether customers that were active 4 weeks ago came back to the website in the subsequent weeks (i.e. relative time filter).
I have a classical useId and sessionId that I could work with.

Anyone has an idea how one could do this? Any help is much appreciated!

Have a look at this cohort plugin viz for Kibana 7.8+
Hope this can help

Hi Yassine,
thank you for your quick reply, unfortunately I am bound the functions provided in elastic cloud. So would there be also a workaround in this environment without plugins?

For each document in your dataset yur need :
@timestamp : the datetime of the event
first_visit_date : the datetime of the first event of the userId
From these 2 fields you will be able to compute the number of days after the first event for evey user and that field can be used with first_visit_date date in the heatMap ...

Check also this discussion