How to map different subdomains to the same directory?

I want to configure multiple subdomains to point to the same directory (document root), but I do not have access to the server configuration (Apache/Nginx). I am using a hosting provider with limited access (shared hosting).

Goal

I have:

• a.example.com
• b.example.com

And I want both to serve content from the same folder, for example:

public_html/myapp

Current situation

• Both subdomains are already created in the hosting panel
• By default, each subdomain points to its own folder

What I want

Instead of separate folders, I want:

• a.example.com → public_html/myapp
• b.example.com → public_html/myapp

Constraints

• I cannot edit Apache/Nginx config (no access to virtual hosts)
• I only have access to:
  • Control panel (e.g., vPanel)
  • File manager / FTP
  • .htaccess

Question

What is the best way to make multiple subdomains point to the same directory in this situation?

• Is there a way to configure this via the hosting control panel?
• Can this be achieved using .htaccess (rewrite or redirect)?
• Or is there another workaround (e.g., symlinks, addon domains, etc.)?