In the manual for the husqvarna 435 chainsaw the screw to tighten the chain is at end of bar (engine end), turn the large knob then adjust the small – and + turn wheel, next tighten back up the large knob.
Here is the full manual download for the husqvarna 435 and the diagram shows you the controls clearly.
On the diagram for husqvarna 435 chainsaws the adjusting screw is on the side of the bar, loosen the large plastic knob then turn the – and + small turn screw to tighten, next tighten the back up the large plastic knob. This should solve it. The chain will slack or loosen with use, especially a new chain so you will have to tighten it every now and then.