A QR code is a square code that can be scanned with a mobile phone camera. They are a bit like bar codes, and I'm sure you've seen them before:
When scanned, they take the user to a particular destination - a web page, or perhaps an application.
A key feature of QR codes is that they are often used in printed material like posters or magazines. Because they exist in the physical world, they can't be changed on the fly if a mistake is found.
Or rather, the QR code itself can't be changed - but its destination can be. At least, it can if the QR code is dynamic.
With a dynamic QR code, as opposed to a static one, the code points to a short URL (or short link) which then points to the destination:
Changing the destination of the QR code simply becomes a matter of changing the destination of the short URL.
There are two ways to create a dynamic QR code. The first way is to use a dedicated 'dynamic QR code' generation tool. However these are often paid-for, or offer a very limited free tier.
For example, QR Code Generator has a free plan that offers one dynamic code - and even the starter plan at $5/month only offers two dynamic codes.
The second way is slightly more complex but more cost-effective. Here, you use a static QR code generator in combination with a URL shortener that lets you change the destination URL after you create a link.
For example, QRickit is a QR code generator that enables you to generate unlimited static codes without payment or even registration.
Rebrandly is a URL shortener (OK, 'link management platform') with a free tier that offers a generous 500 branded links.
Using the two in combination, it is possible then to create 500 dynamic QR codes absolutely free of charge.
Simple create your short URL in Rebrandly, then use that short URL in QRickit to generate your QR code. Even after your code has been published and distributed, you will be able to change the destination by editing the link's destination back in Rebrandly.