Can I get a source code to make the ESP module (which is in a wemos d1 mini in my case) act as an AP please?
You don't even NEED any code to make an ESP_Basic device act as an AP (Access Point), because that is what it does by default even with no script loaded.
To even ask such a question suggests you haven't read any of the getting started info, so here's a brief pointer to getting you started...
Download the ESP_Basic flasher executable and run it as administrator.
Boot your D1 mini into flash mode (by grounding D3 at powerup/reset)
Select the appropriate Comm Port and Flash Memory Size from their dropdown lists, then click the big Firmware Flash button.
When the blue led stops flickering, the device will take about 30 seconds to automatically reboot back up as an ESP_Basic AP, which should appear in the 'available wifis' list as ESP something or other (most likely ESP + the devices MAC address).
Choose connect to that wifi device name, after connected, browse to 192,168.4.1 and you should then be connected to your new ESP AP. From that page you can Edit scripts (try copying and pasting in some examples), Save edited scripts (upload them to the ESP), then Run then remotely on the ESP device.