The first thing to do is to speak to your medical team They will know any suitable clinical trials at the centre where you are being treated, and may be aware of others elsewhere that you may be eligible for.
If you are enquiring about trials at a different centre to the one you are being treated at make sure you are able to tell them your type of tumour the grade and, for drug trials, the type of genetic mutations your tumour has. Your medical team will be able to supply this information after they have taken a biopsy- and possibly following an MRI scan.
You can try searching online using your tumour type and the country in which you are looking for a clinical trial. The UK based NHS resource Be Part of Research is an excellent place to search for UK based clinical trials for brain tumours or your search could be expanded to include Europe with The European Union Clinical Trials Register and the US with ClinicalTrials.gov.
Also online you can register your interest in UK based brain tumour research so that researchers can get in touch if they begin a suitable study. National Institute for Health Research (NIHR) BioResource is one such resource and others, as well as further information on UK based research into brain tumours can be found on our website.