What to do if there are signs of dehydration?

When to suspect

Recent increase in diuretics.
Progressive weight loss under diuretic therapy.
Additional pathology causing anorexia for more than 1 day, inability to eat or drink, vomiting, diarrhea, fever, etc.

Interrupt diuretics (diuretics, MRA, SGLT2 inhibitor) and in case of hypotension and/or renal insufficiency ACE inhibitor/ARB / ARNI.
Encourage sufficient drinking with re-evaluation after 2-4 days. After recovery of blood pressure and renal function, always try to quickly restart the interrupted heart failure therapy at 25% or 50% of the previous daily dose, initially without diuretics and in a lower dose, with an uptitration back to the normal maintenance dose over days to a few weeks to the therapy like before the event.
Hospitalization for intravenous fluid therapy and further exams is certainly indicated in case of drowsiness, symptomatic hypotension, significant renal insufficiency, inability to eat and drink, etc.