My samsung S21 is not connecting with second sim

[Peculiar]

 My Samsung S21 second sim is not showing on my phone after I did the factory settings

[Piper123]

Hey there and welcome to the Samsung UK and EU Community Forum

We will need a bit more from you on this.

What exactly happened and when?

Have you checked that the second SIM is correctly inserted and is active?

[Peculiar]

Yes, I have checked, although it was working properly before I did a factory reset due to an annoying sound it was making

[Banonar]

Maybe dust, or it's a bit loose.