Need advice on how to approach a girl I recently saw

I (26M) saw a girl one week ago. She works as a receptionist in a hospital. I went there for my sister's health check up. Instantly, I got a liking for her because of the way she speaks, her smile, and how sweet she looks. I couldn't take my eyes off her most of the times. She also noticed it. Later, while she was leaving the hospital, coincidentally I was coming from the way. She smiled a bit while looking at me, I aslo smiled back. But, then I got a call and suddenly took a right turn and went away. I couldn't get her off from my mind since then. One week later (today), I went near the place where she seats in the hospital even if there was no reason for me to visit there. Except talking to her. But, I miserably failed to build up the courage to talk to her. I even waited outside the hospital for her shift to get over, but my sister came and I had to go to the market with her. I missed the opportunity today also😭😭. I will be going home tomorrow which is 400 km away from that hospital. I might come after one week, but how should I go about talking to her?? Should I go and talk to her in the hospital or outside?? Good people of reddit please help your single brother!!! For context, I never had any gf nor did I approach any girl till now. P Note: posting it again as the previous post was removed.