Hi @thilary311,
Unfortunately your model phone doesn’t have any options to extend the ringing time. You can only temporarily silence the ringing signal for one call. The phone will ring again on the next call.
If you have a Voicemail feature connected to your landline phone service you may be able to extend the ring time before the call diverts to the Voicemail box. It might depend if you are on the maximum amount of time already or not. Usually it defaults to a lesser time, so you may be lucky
You would have to check on your landline phone service provider’s website how to do this as each provider has their own method. Alternatively, contact your landline phone service provider’s customer service section and ask them.
If you don’t have the Voicemail feature connected to your phone service then the ringing time ''may'' be adjustable, but again you would have to check with your landline service provider as above.