How to replace a joomla web with WordPress?

Dear Friends,

I’m facing a technical confusion !

Problem
One of our client want to purchase a WordPress theme and do a fresh installation on server ! (This can be done easliy)
but the old website is working with joomla and it has around 8 other websites running on its “subfolder”
eg : https://www.example.com ( main web) , https://www.example.com/abcd, https://www.example.com/1234 etc
all web is working on joomla.

My task
I have to install and develop the main web ,and connect the other webs as it is

how to reconnect the sub installations on WordPress ?

eg : https://www.example.com ( will run on wordpress ) but can’t change the subdomains which is running on joomla

it should work as https://www.example.com/abcd even after the installation

Could you help me ?

Thanks in advance !

Links : (https://www.nispana.com) has to install wordpress , Sub domain, can’t change any installation (https://www.nispana.com/buildindiasummit/)