You’ve not provided many details, so I’ll have to make assumptions.
I’m going to guess the list of addresses above corresponds directly to the Walks inline table below.
I’d guess the date is the row label, and that the list of dates in the deck view comes from the system-generated column with an App formula expression that uses REF_ROWS(), probably having a name beginning with “Related”.
The order of the rows in the inline table in the details view is determined by the configuration of the table view with a name probably ending with “_Inline” in the ref position for the (data) table containing those rows.
The order of the dates in the deck view, presumably coming from the REF_ROWS() column mentioned above, is undefined: they’re in no intentional order, they just happen to be in (what appears to be) chronological order, earliest to latest. It sounds like you either want them sorted in reverse chronological order (latest to earliest), or you just want the latest.
To order the dates in the deck view in reverse chronological order, edit the current REF_ROWS() expression to wrap it with ORDERBY(). For instance, if it’s currently this:
REF_ROWS("Walks", "Dog Id")
change it to something like this:
ORDERBY(REF_ROWS("Walks", "Dog Id"), [Walk Date], TRUE)
Dog Id should be replaced with whatever values are already in the current REF_ROWS() expression, and
Walk Date should be replaced with the name of the column in your walks table that contains the date of the walk.