This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 臶 is uncertain. It visually combines 至 and 存, but the original semantic or phonetic role of these components is unclear.
Since the meaning is unclear, focus on the shape: 至 (arrive) and 存 (exist) side by side. Imagine something arriving and existing together, but treat the meaning as unknown.
For セン, use the common reading of 千 (せん, thousand) as a hook: picture a thousand uncertain meanings arriving and existing together in this rare kanji.