Hey @prashant,
I would suggest reading Building your own Flowable Spring Boot application blog post and checking out our spring-boot example.
The reason why you are not seeing the REST APIs is because you do not have the needed dependencies on the classpath.
You need:
<dependency>
<groupId>org.flowable</groupId>
<artifactId>flowable-spring-boot-starter-process-rest</artifactId>
<version>6.5.0</version>
</dependency>
in order to have the rest APIs for the process engine available