Access to an MCP server can expire over time. What you do depends on how you connected, so here are both paths.
If you connected with authorization
Mando refreshes access for you in the background. If it cannot, the card shows a Needs reconnection state with a Reconnect button. Click Reconnect and approve access again in the window that opens. Your tools and selection come back.
If you connected with an auth key
A static key has no reconnect prompt. When the key stops working, calls just start failing and Test Connection reports the error. Disconnect the server, then connect again and paste the current key.
After reconnecting
Run Test Connection and send a test message to confirm the tools work again. Your saved tool selection is kept.