Gradle sync failed: Could not find com.android.tools.build:gradle:5.5.1

This dependency corresponds to the Android gradle plugin, not Gradle itself. Typically, the Android gradle plugin should match the version number of your Android Studio installation (e.g. "3.4.2").

If you want to update Gradle itself, and you are using the gradle wrapper, update the gradle/wrapper/gradle-wrapper.properties file and edit the distributionUrl line:

distributionUrl=https\://services.gradle.org/distributions/gradle-5.5.1-all.zip

If you are using a local distribution, then you don't have to do anything. Your project will be built using the gradle distribution set in the Android Studio settings (in your case, Gradle 5.5.1).

Edit: It seems that your build.gradle file is also missing the google() repositories, here is what it should look like if you want to use the Android gradle plugin 3.4.2:

buildscript {
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.4.2'
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}