If you want a quick and dirty fix add some sealant to the joint; CT-1 or similar. Won’t stop water pooling but it will stop it leaking.
That's what I've done, along with repositioning the guttering as it wasn't overlapping enough. I'd say it's stopped 90% of the water but definitely isn't a long term fix.
@Howard started
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If you want a quick and dirty fix add some sealant to the joint; CT-1 or similar. Won’t stop water pooling but it will stop it leaking.