If you allow debris to gather inside the downspout it will eventually clog and it will cause overflowing and eventually damage to the house. This is not a problem that can be passed away.
First get a ladder and climb up the house to reach the mouth of the downspout and gutter.
Use a piece of wire inside the gutter all the way down to try and loosen the clog. Move the wire from side to side and try to move the clog. Any debris that lay on the top of the downspout can be removed with tongs. All the dirt that you accumulate should be placed into a bucket.
Climb again on the ladder but this time with a turned on hose. Start pouring water down the downspout and hopefully all the work you did earlier will have loosened the clog making it get out of the downspout to the ground because of the water pressure. Don’t stop pouring water until you remove all the dirt.