move, shift, change, transfer, relocate a capital city
迁 centers on movement from one place to another: moving, shifting, changing location, or transferring something. The specific sense of relocating a capital city is a formal application of that same idea.
迁 combines 辶 (movement) with 千, which likely contributes the sound and may suggest a large-scale movement or change. The exact historical development is uncertain.
The movement radical 辶 wraps around 千 (thousand). Picture a thousand people moving together, shifting their entire settlement to a new capital.
For セン, imagine a thousand (千, せん) people moving along a road: 千 -> セン, and the whole crowd shifts together.