You can find the full series of Zindagi Gulzar Hai available for free and legal viewing on the official HUM TV YouTube Channel
Here are the primary reasons fans prefer a single file download: Zindagi Gulzar Hai All Episodes In One File Download
If you absolutely must have a local copy, download each episode legally via YouTube Premium or Netflix offline mode, then use a video merger tool to combine them yourself. It takes an extra 10 minutes, but you sleep better at night. You can find the full series of Zindagi