Hello Nimish,

IMO is conducted by SOF, therefore previous year question papers are available on there websites, you may head over to the below link:

https://www.sofolympiadtrainer.com/imo-previous-year-papers.jsp

http://www.sofworld.org/imo-previous-year-papers-rtp.html

For practise and sample papers prepared by SOF,refer the below links:

https://www.sofolympiadtrainer.com/imo-sample-papers.jsp

And below is the sample IMO paper for class 1

http://www.sofworld.org/imo/class-1/sample-model-test-papers/imo-sample-papers-class-1

Hope this Helps

Regards