You need to use the reset function of SplitInBatches. It’s not totally obvious and could do with some documentation - Split In Batches - n8n Documentation
The key is changing the reset parameter in your SplitInBatchesMessages node to {{$node["SplitInBatchesMessages"].context["noItemsLeft"]}}. Once its batch of RSS messages has finished it resets the state of the node ready for the next set of RSS feed messages.
If you want to collate all the data afterwards, you’ll need to use a function node to merge the 3 executions together, see https://n8n.io/workflows/1160/
P.S. you’re not dumb 