have a motor actuator md120-01-l2-416-091 Input DC18-35V 5A MAX want to increase speed, what do I need to use to accomplish this
Assuming this is a brushed DC motor, you'll need to increase the voltage driving it. Since it is an 18-35 volt motor, I'd guess you're using a 24 volt battery. If so, you are out of luck unless you can provide a higher motor voltage. If you can find a 5 amp, 24 to 32 (or so) DC-DC converter, you could use that. Drive the converter from the battery and use the converter output to drive the motor. These converters are actually fairly common, and if you search on "dc-dc converter 32v" on eBay you'll find lots of cheap units which have the necessary specs. 2 warnings, though.

1) Cheap Chinese electronics parts are, well, cheap Chinese parts. They don't come with any sort of money-back guarantee, and you can't sue them if it doesn't work as advertised. Buyer beware.

2) Cooling/airflow on a converter is a must. If the converter overheats it can quite possibly cause the chair to catch fire.