The plugin has a java api that can be used from scripts.

The example below demonstrates the basic api methods.

import com.atlassian.jira.component.ComponentAccessor
import com.jibrok.jira.plugins.banner.service.BannerService
import com.jibrok.jira.plugins.banner.dto.BannerDto
import com.onresolve.scriptrunner.runner.customisers.PluginModule
import com.onresolve.scriptrunner.runner.customisers.WithPlugin

@WithPlugin("com.jibrok.jira.plugins.banner")
@PluginModule
BannerService bannerService

List<BannerDto> banners = bannerService.getAll()

BannerDto bannerWithId4 = bannerService.get(4)

BannerDto newBanner = new BannerDto(
    [
        users: ['admin'],
        groups: ['jira-software-users'],
        message: """
<a>test link</a><br>
message
""",
        color:"#4287f5",
        start: new Date(),
        stop: (new Date() + 1)//+ 1 day
    ]
)
bannerService.create(newBanner)

BannerDto updateBanner = new BannerDto(
    [
        id:4,
        message: """<a>test link</a><br>message""",
        color:"#f2f542"
    ]
)
bannerService.update(updateBanner)

bannerService.delete(6)