Heya @MattGCDT
Ok, so firstly, I hope you have a column that references the relationship between the tables - this could be something like ReptileID in your list of Reptiles, and then ReptileID in your list of service records - that will enable us to filter between the two when one is chosen.
So you've said you have a list showing your list of reptiles, and you want that when you select it, it then goes to another screen to show a list of records relating to that reptile.
Ok so our first screen we have a gallery listing all of the reptiles. the OnSelect of the Title object within the gallery is likely set to Select(Parent) at present as that is the default - we can leave that as it is, and then edit the OnSelect property of the gallery itself (click on the gallery in the left-hand-pane, then above that, choose OnSelect from the properties dropdown).
Now we can change this OnSelect property to:
Navigate(YourRecordDetailsScreenNameGoesHere)
Then in your Record details screen, we have another gallery, its Item should be set to the Service Records list. We will then edit the Items property to filter that gallery by what you have chosen in the first gallery (we will call this gallery1 as that is what Power Apps will likely call it by default).
Items property for this second gallery then becomes:
Filter(ServiceRecordsListNameGoesHere, ReptileID = gallery1.Selected.ReptileID)
This should now show a filtered list of Service Records based on what reptile you chose in the first gallery.
Cheers,
Sancho
