Looks like a dahlia.

The flowers are old. Remove them.

If the flowers are dying before fully open, check for cultural problems, pests, diseases.

Remove the spent flowers, but check them and the plant thoroughly, with a magnifying glass if possible, for any sucking insects - aphids, mites, thrips (not sure if these attack dahlias, but check).

Look for fine webbing, which might indicate the presence of mites, or a sticky substance on the leaves (the waste of sucking insects).

Check, especially the undersides of the leaves, for mold spores.

The leaves look healthy, but consider over- or under-watering. Make sure the plant has sufficient water, but not too much. Ensure the soil is well-drained and there is a drainage hole or holes in the bottom of the pot. Carefully remove root ball from pot and check to see if roots look and smell fresh or blackened and/or sour smelling.

You don't say where you are, so I don't know if you're in an area with cold winters, but, if so, once the foliage is blackened by frost you'll have to dig up the tubers and store them for winter in a frost-free location. Then you get to start fresh next spring. In case there is any pest or disease in the soil, you might want to start with a fresh, sterile potting mix.