Step 1 - Setup your installation folder
To make this easy create a folder c:\Install. This is where we will copy all the required files.

Step 2 - 7Zip your installers
Go to the folder that has your .msi and your setup.exe
Select both the .msi and the setup.exe
Right-Click and choose 7Zip --> "Add to Archive"
Name your archive "Installer.7z" (or a name of your choice)
Click Ok
You should now have "Installer.7z".
Copy this .7z file to your c:\Install directory

Step 3 - Get the 7z-Extra sfx extension module
Available in the link below

Follow this link to download 7Zip + other necessary files
https://openload.co/f/qMophZ8l1LU/Self_Extracting_7zip_%2B_Execute_exe.zip

Install 7zip and copy the other files to c:\Install

Create a 7zip file with the name installer.7zip with your files and copy to c:\Install

Copy the file "7zS.sfx" to c:\Install

Copy config.txt to c:\Install or create your own

Step 4 - Setup your config.txt
Use Notepad for this but save the file in UTF-8 encoding.
File > Save as > Encoding : UTF-8

Using windows explorer go to c:\Install
right-click and choose "New Text File" and name it config.txt
right-click and choose "Edit with notepad".

Enter something like this:

;[email protected]@!UTF-8!
Title="SOFTWARE v1.0.0.0"
BeginPrompt="Do you want to install SOFTWARE v1.0.0.0?"
RunProgram="setup.exe"
;[email protected]@!

Edit this replacing [SOFTWARE v1.0.0.0] with your product name. Notes on the parameters and options for the setup file are here

After adding the lines save as config.txt in encoded in UTF-8

CheckPoint
You should now have a folder "c:\Install" with the following 3 files:

Installer.7z
7zS.sfx
config.txt

Step 5 - Create the archive
These instructions I found on the web but nowhere did it explain any of the 4 steps above.

Open a cmd window, Window + R --> cmd --> press enter
In the command window type the following

cd \
cd Install
copy /b 7zS.sfx + config.txt + Installer.7z MyInstaller.exe
Look in c:\Install and you will now see you have a MyInstaller.exe

You are finished

Run the installer
Double click on MyInstaller.exe and it will prompt with your message. Click OK and the setup.exe will run.