In case you need purely outpatient treatment (without an actual admission to hospital), these ambulatory (outpatient) medical expenses are eligible for reimbursement if you are affiliated to an ambulatory guarantee. The reimbursement conditions of your ambulatory guarantee remain applicable. You submit these medical expenses via the usual tools and ways.
The hospitalisation guarantee only covers ambulatory medical expenses that are directly related to an accepted hospitalisation. Therefore, ambulatory medical care in quarantine is not eligible for reimbursement under the hospitalisation guarantee. The expenses for the corona test itself are reimbursed by the Belgian national service for medical and disablement insurance (RIZIV) for that matter.