In a randomized controlled trial of 12.5mg bid losartan in 117 COVID-19 outpatients, a treatment effect of larger than a 4.8% absolute decrease in hospitalization was ruled out. Due to lower than expected hospitalization rates, the trial was terminated early for futility.

List of Angiotensin-receptor blocker (ARB) trials for COVID-19:

The first randomized controlled trial of an ARB for treatment of COVID-19 returned preliminary results showing possible improvements in time to discharge, need for supplementary oxygen and CRP. See "Telmisartan for treatment of Covid-19 patients: an open randomized clinical trial. Preliminary report." See independent critical appraisal of trial.
In a small (n=80) randomized controlled trial of de novo initiation of losartan 25mg bid versus 5mg amlodipine in ACEi/ARB-naive hospitalized patients presenting with hypertension, no statistically significant difference was seen in the primary outcomes between the groups; however, the losartan group appeared to have improved outcomes (not statistically signifiant).

ACE inhibitor trials:

While not a trial of ARBs as therapy, BRACE CORONA was a randomized controlled trial exploring stopping-versus-continuing ACE inhibitors/ARBs in patients with hypertension. It showed no harm in continuation of ACE inhibitors and ARBs with COVID-19. There was a non-statistically significant hint of a benefit in the ACEi/ARB group but the trial was not powered to detect this.

Other trials of renin-angiotensin modulation for COVID-19:

In a double-blind, randomized, placebo-controlled trial of AT2R agonist C21, one patient in the C21 group required supplementary oxygen at day 14 versus 11 patients in the placebo group (p=0.003). 
C21, an AT2R agonist, has shown benefit in animal lung injury models, similar to ARBs. In a recent randomized, placebo-controlled clinical trial, C21 showed promise as COVID-19 treatment. Photo CC-BY Rathinasabapathy, et al.

See also