How to get second brood in nest box?

[Norfolkandchance]

Hi, we have a nest box with a camera in it. Much loved by my family. However, the last two years we have blue and great tits and both have built a nest, laid eggs then, after being very attentive, disappeared, presumed eaten.
Given that there is plenty of time for a second pair to use the box. Is there anything we can do to encourage this. Remove old eggs? Whole nest?
Thanks