Hi,
I have router configured as LTE using mobile date.
How can I change that internet will be connected to one of the port.
I pulled fiber optic cable and now have the possibility to use ethernet cable.
Many thanks in advance 
I’m not sure exactly what you’re trying to do since you mention fiber and LTE.
For LTE, if you want the modem to go DIRECTLY to a port (thus not routed or available to the MikroTIk), you can use “passthrough”. See docs:
https://help.mikrotik.com/docs/spaces/ROS/pages/30146563/LTE#LTE-PassthroughExample
If you’re changing from LTE to fiber, you’d need to remove the SFP from any bridge, add a DHCP client (or assign WAN IP statically) and add the interface to WAN interface list – assuming you have the default firewall from home/SMB routers. If you have a bigger router (one without a default firewall) or want BOTH LTE & fiber, more detail be needed.
Maybe there is a ISP device converting from fiber to ehernet, as ethernet cable is mentioned.
If this is the case, the procedure is the same, only instead of sfp you make sure that ether1 is out of the bridge, categorized as WAN and has a DHCP client running.
Anyway it would be much better/easier if you could post more details on your layout and your current configuration, following these instructions:
http://forum.mikrotik.com/t/forum-rules/173010/1
If I got paid a nickel every time you typed that…
One day you too will see the light of a sandbox for new users…
Well, it doesn’t work that way, I write the posts, I get the pennies. 
Maybe one day …
https://c.tenor.com/AkV47FRnjHIAAAAd/tenor.gif
my guess would be that OP has an MT with LTE capabilitiies, that also has some ethernet ports, and is used as switch, and now he ALSO has internet connectivity on ethernet side (likely via other means). fiber convertor or FTTH “modem” or something. so.
my 2 cents would be a suggestion to use one ethernet port as an uplink with NAT and stuff as usual and watchdog for that connectivity, if it is going down, switching to LTE. other hints and config examples are welcome.
That is the point, there should not be three people guessing, it should be one person answering correctly for a decently constructed post. Rinse repeat posts per day, day after day, year after year…
Definition of insanity or refusal to look at context…
you say it like you’ve never worked for support, translating from human to techspeak 
everybody is lazy and writes/tells minimum-minimorum of information, expecting others sharing same context and common sense… which is not that common.
I love it
The point is the lethargic morons that run the forum dont understand the value in a very easy fix, and building momentum to make some changes is made more difficult by a lazy apathetic bunch of forum users, who sadly accept the insanity of the situation as almost a given. 